Household refrigerators generally comprise an outer metal case and at least one inner liner insulated from the case and defining a refrigerated food storage compartment. Due to leakage through the insulating means separating the outer metal case from the liner or due to refrigerated air leakage past the door sealing means, portions of the outer metal case adjacent the access opening to the storage compartment tend to fall below the dew point of the surrounding atmosphere causing the accumulation of moisture in these areas. To prevent such condensation, suitable heating means such as an electric resistance heater, generally known as anti-sweat heater, have been provided to maintain the temperature of the case area adjacent the access openings sufficiently warm so that such condensation does not readily occur. The heating means generally employed has been a low wattage electrical resistance heater connected directly across the power supply lines so as to be continuously energized regardless of whether the refrigerating means for cooling the storage compartment is operating or not. This kind of arrangement, however, can use electrical energy unnecessarily.
Various alternative arrangements to reduce the electric power consumption of the anti-sweat heaters have been used in the past. For instance, U.S. Pat. No. 3,939,666 discloses an electrical control circuit that, when the refrigeration system is not in defrost and there is a high humidity condition, the mullion heater utilizes full power and the stile heater utilizes half electrical power. In the case of low humidity and, again, the refrigerating system is not in defrost, the mullion heater utilizes half electrical power and the stile heater uses no electrical power. When the refrigerating system is in a defrost condition, both the mullion and stile heaters are "off". This arrangement, however, controls power to the heaters by means of a humidity sensor. It does not control the electrical power to the anti-sweat heaters responsive to the compressor operation which is an important aspect of the present invention. When the compressor of the refrigeration system is "on", there is inherently produced more cold air leakage from the refrigerated compartment than when it is "off". However, there is still some reduced amount of cold air leakage that will produce condensation when the compressor is "off".
U.S. Pat. No. 2,135,091 discloses energization of the anti-sweat heaters at full electrical power either only when the compressor of the refrigerating system is operating or all the time when the system is operating.
There is also a prior art arrangement that utilizes a manually operated switch for half electrical power, full electrical power, or no electrical power for the anti-sweat heaters which selection must be made by the user of the refrigerator.
It is desirable in a household refrigerstor, to have the anti-sweat heaters automatically controlled during operation of the refrigeration system so that when the compressor is "on", full electrical power will be supplied to the anti-sweat heaters and when the compressor is "off", only half electrical power will be supplied to the anti-sweat heaters. By my invention, there is provided a refrigerator, including anti-sweat heaters, having a control circuit which will accomplish these desirable results.